1. Field of the Invention
The present invention relates to a channel code in a wireless communication system.
2. Description of the Related Art
To perform low complexity decoding, conventional art assumes a Gaussian distribution of an interference signal. Therefore, a modulation method of a Quadrature Amplitude Modulation (QAM) series is commonly used to approximate a characteristic of the interference signal to a Gaussian function (or Gaussian).
However, it is widely known that a non-Gaussian channel actually has a bigger channel capacity than a Gaussian channel. Consequently, if decoding is properly performed, a non-Gaussian channel can provide greater decoding performance than a Gaussian channel.
Accordingly, research has been conducted on a modulation method in which an interference signal follows a non-Gaussian distribution. For example, a proposed modulation method is Frequency-QAM (FQAM), which is a hybrid modulation method combining QAM and Frequency Shift Keying (FSK). FQAM has all the merits of increasing a spectral efficiency of the QAM and making an interference signal of the FSK non-Gaussian.
If a QAM series is used for modulation, generally, a statistic characteristic of an interference signal follows a Gaussian distribution. As a result, it is common that one code, which is optimally designed considering an Additive White Gaussian Noise (AWGN) channel, is used in a system. Accordingly, a Base Station (BS) and a terminal have information about a channel code of one kind in accordance to a given modulation method and coding rate.
However, if FQAM is used for modulation, a statistic characteristic of an interference signal follows a non-Gaussian distribution, and a code having optimal performance can differ, based on a non-Gaussianity of a channel. Therefore, when only one channel code is used, as in the conventional art, if the used channel code is a code optimized to a channel having small non-Gaussianity, decoding performance may deteriorate in an environment having higher non-Gaussianity.
Basically, a channel code that is optimized for an environment in which an interference signal follows a Gaussian distribution may not provide the same optimal performance in a non-Gaussian channel. Similarly, a channel code optimized for an environment in which an interference signal follows a non-Gaussian distribution may not provide optimal performance in a Gaussian channel.